Re: Beat grouping and reverting

[Neil Puttock]

Hi Trevor,

2008/10/25 Trevor Daniels <address@hidden>:
> Carl
>
> But how do you revert entries like this:
>
> ((end * * 6 8) . #f) ;; switch-off at-any-beat feature

The simplest way would be to add a function to switch this back on:

#(define (revert-property-setting context property setting)
  "Like the C++ code that executes \revert, but without type
checking. "
  (define (revert-member alist entry new)
    "Return ALIST, with ENTRY removed.  ALIST is not modified, instead
a fresh copy of the list-head is made."
    (cond
     ((null? alist) new)
     ((equal? (car alist) entry) (revert-member (cdr alist) entry new))
     (else (revert-member (cdr alist) entry (cons (car alist) new)))))
  (ly:context-set-property!
   context property
   (revert-member (ly:context-property context property) setting '())))

#(define (allow-at-any-beat num den)
  (ly:export
   (context-spec-music
    (make-apply-context (lambda (c)
                          (revert-property-setting
                           c 'autoBeamSettings
                           (cons `(end * * ,num ,den) #f))))
        'Voice)))

\relative c'' {
  #(set-time-signature 6 8 '())
  #(allow-at-any-beat 6 8)
  #(revert-auto-beam-setting '(end * * 6 8) 3 8)
  #(revert-auto-beam-setting '(end 1 32 6 8) 1 8)
  #(revert-auto-beam-setting '(end 1 32 6 8) 1 4)
  #(revert-auto-beam-setting '(end 1 32 6 8) 1 2)
  #(revert-auto-beam-setting '(end 1 32 6 8) 5 8)
  a8 a a a a a
  \set beatGrouping = #'(2 2 2)
  a8 a a a a a
}

A better solution might be to rewrite revert-auto-beam-setting so that
the args for beat begin/end are moved to the optional argument list
(which is currently only used for the context).

Regards,
Neil

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